1. Field of the Invention
This invention is generally directed to the formation of molded sheets, panels, or the like having a textured surface. More particularly, the present invention relates to a novel and improved method of forming plastic castings or the like made of a suitable polymerizable hydrophobic monomeric material having a randomly textured surface.
2. Description of the Prior Art
In the field of casting polymerizable materials, it is generally known to provide at least one surface of the cast material with a textured surface. In many situations, this is primarily performed for purposes of enhancing the ornamental characteristics of a molded piece of material, as well as improving light diffusing properties of certain materials, such as those made from acrylic resins.
Several rather well-known techniques exist in the art for providing cast materials with textured surfaces. Generally speaking, the earlier attempts for obtaining such a surface were achieved by etching, embossing, blasting and the like. Later, other attempts contemplated pre-embossed polyester films, such as taught in U.S. Pat. No. 3,072,973. These latter prior art methods, as with the type indicated above, suffer, however, from the common disadvantage of being relatively complicated and expensive procedures.
Another heretofore known approach, disclosed in U.S. Pat. No. 3,306,956, essentially aims at producing decorative cured resin panels and the like through a single casting or pouring step. In this patent, however, a thin sheet of film is mechanically creased prior to molding so as to provide a multiplicity of elevated and depressed parts in the finished casting. Such mechanical creasing of the film is usually accomplished by crumpling, crushing, squeezing, and drawing the film. The particular disadvantage associated with the foregoing described method, is that the textured surface must be produced by a mechanically pre-formed and pre-distorted pattern sheet or film. Although this process provides an improvement over conventional procedures, it nonetheless is not altogether satisfactory from the standpoint that it requires the additional step of mechanically pre-forming the film to achieve a desired surface having a multiple, irregular and random pattern. This additional step, in general, also undesirably results in a textured casting which is relatively expensive to produce.
It should be emphasized that the particular field of casting panel members or the like having a textured surface is extremely competitive, and there is a small profit margin associated with the production of these textured panels. As a consequence thereof, it will be appreciated that even slight increases in costs may render such panels commercially less desirable from a cost standpoint than the competing materials.
Further known methods for producing a textured surface during a single step casting step are generally disclosed in U.S. Pat. Nos. 2,288,559 and 3,269,886. As described in the latter patent, a cementitious material which is to be molded incorporates water which reacts with the cementitous mass to set the same and also reacts upon a film of material so as to cause the film to swell at the same time the cementitious material is brought into contact with the film. A major disadvantage associated with this particular casting method is that it depends upon a swelling operation resulting from water absorption to produce the non-uniform surface pattern. Consequently, such teachings would be unsuitable for casting non-uniform patterns in hydrophobic materials, such as, for instance plastics.
In connection with the earlier referenced U.S. Pat. No. 2,288,559, a wax paper film of material is described as being inserted in the mold so as to serve to distort the fluid mass of material during hardening. As with the previously mentioned prior art technique disclosed in the above patent, this particular patent similarly suffers the shortcoming of being limited to those situations wherein hydrophilic masonry or concrete type materials are employed. It would not be suitable to provide for the formation of a random textured surface for hydrophobic materials, such as a polymerizable acrylic monomer. Similarly, the process defined in U.S. Pat. No. 1,588,728 is subject to the disadvantage that it is primarily intended for use in conjunction with hydrophilic materials. Accordingly, it could not be effectively used with hydrophobic materials.
As can be appreciated from the foregoing comments directed to the typical shortcomings associated with the formation of cast materials having textured or patterned surfaces, none have, in general, been able to successfully achieve in a simple, reliable, and economical manner the production of randomly textured surfaces on finished cast members made from a hydrophobic material, such as polymerizable acrylic monomers by using a thin shrinkable plastic sheet, such as polyethylene.